ALPHA-FLOW Interface

Solver Alpha-Flow
Type of mesh structured, cartesian or cylindrical mesh
Dimension 2D and 3D



This interface writes a grid and boundary condition file for ALPHA-FLOW. ALPHA-FLOW can deal with Cartesian, cylindrical and body-fitted single-block grids (O-grid, H-grid, C-grid and L-grid).

For Cartesian or cylindrical coordinates grids, a single ASCII file (called "Input data file for solver") is written. It contains the number of stations in each direction, the list of these stations, and the description of 2D and 3D partial regions such as obstacles, initial patches and boundary conditions. User-defined name can be given to these regions for set-up obstacles or patches initial condition.

In the case of body-fitted grid, two files are required. The grid coordinates are written in Fortran binary to a file called "BFC grid file". Additional information such as the grid dimensions, the description of 2D and 3D partial regions, and the indices of degeneracy (H-grid) are written separately in an ASCII file.

This ALPHA-FLOW output interface supports four types of grids:

Creating the ALPHA-FLOW input file(s)

The body-fitted grids can be generated with the HEXA-Mesher, option Multiblocks. One or several structured domains can be used as input for the BFC translators (compressible or incompressible). If several blocks are used, they are converted internally to a monoblock grid prior to writing the BFC grid file. Note that the ALPHA-FLOW translator does not accept a superdomain file as input. This is due to the particularity of ALPHA-FLOW H-type grids, which require the insertion of additional cells at the degenerated faces. The regular ICEM-Superdomain program does not support such grids. Therefore, the ALPHA-FLOW translator has its own multiblock to monoblock converter.

The cartesian and cylindrical grids can be generated with the GLOBAL-Mesher. From the GLOBAL-Mesher GUI, make sure to save the grid with the option "Staircase-Volume".

Once the grid is generated, the translator may be called from the main GUI. Simply select "ALPHA-FLOW" from the list of translators in the "Output" menu. After selecting the command "Write Input" from the same menu, a window opens up listing the options for the ALPHA-FLOW translator:

The interface generates the ALPHA-FLOW files in the project directory.

Defining partial regions and obstacles

For 3D models, partial regions and obstacles may be defined on blocks (3D) or faces (2D). For 2D models, partial regions and obstacles may be defined on faces (2D) and edges (1D). For grids generated with the HEXA-mesher, partial regions and obstacles are composed of one or several families. For details on how to set boundary conditions and properties, please refer to the document "General Remarks".


To define a named region, select an entity then specifies its region_name. All entities with the same region name are written in the same BLOCK in the Input data file.

    1.string1        Enter NAME
    2.string2        Enter the region name (5 char. max.)      

Obstacles for BFC-Compressible, Cartesian and Cylindrical Grids

To define an obstacle, select an entity (family, subface, edge or family) and assign to it the character string OB, in the appropriate field of the boundary condition menu. If the non-continuous surfaces in the computational space are treated to vary smoothly, specify YES in the second character field (see below). By default, 'NO' is written for each obstacle in the input data file.

    1.string1        Enter OB 
    2.string2        Enter YES, if applicable (optional)

Obstacles for BFC-Incompressible Grids

For BFC-grids for incompressible solver, two types of obstacles can be defined:

For a bidimensional grid, slab-type obstacles are applied to surfaces and slit-type obstacles to edges. For a tridimensional model, they are applied to blocks and faces respectively.

    1.string1        Enter SLIT or SLAB

Special tagging for H-type topology

For H-type grids, if zero-volume cells need to be generated along an edge or a face, this edge or face needs to be tagged CELL. So, whenever the index of degeneracy is equal to 1, the boundary of the obstacle is tagged with SLIT and the boundary of the zero-volume cells is tagged with CELL.

    1.string1        Enter CELL